Dairy Products Wastewater Treatment System Process Description

The dairy industry involves processing raw milk into products including milk, butter, cheese, yogurt, using processes such as chilling, pasteurization, and homogenization. Typical by-products include buttermilk, whey, and their derivatives. Huge amounts of water are used during the process producing effluents containing dissolved sugars and proteins, fats, and possibly residues of additives. These effluents have the following characteristics

Biochemical oxygen demand (BOD), with an average ranging from 0.8 to 2.5 kilograms per metric ton (kg/t) of milk in the untreated effluent

Chemical oxygen demand (COD), which is normally about 1.5 times the BOD level

Total suspended solids (TSS), at 100–1,000 milligrams per liter (mg/l)

Cream, butter, cheese, and whey production are major sources of BOD in wastewater. The waste load equivalents of specific milk constituents are: 1 kg of milk fat = 3 kg COD; 1 kg of lactose = 1.13 kg COD; and 1 kg protein = 1.36 kg COD. The wastewater may contain pathogens from contaminated materials or production processes. A dairy often generates odors and, in some cases, dust, which also need to be controlled. Hydro-Flo engineers and builds complete solutions to efficiently manage the wastewater treatment and odor control requirements of the dairy industry. Our solution includes the following benefits:

Optimization of use of water and cleaning chemicals with option for recirculation of cooling waters.

Segregation of effluents from sanitary installations, processing, and cooling (including condensation) systems; this would facilitate ability to recycle the wastewater.

Energy recovery through use of heat exchangers for cooling and condensing.

Use of high-pressure nozzles to minimize water usage.

Dairy wastewater is treated by adjusting pH and using strong coagulant chemistry to break any emulsions caused by cleaning agents and sanitizers and to precipitate solids and fats. The chemicals are added to cause de-emulsification, precipitation, coagulation, and flocculation.

The reuse of wastewater from the dairy industry can also be provided for by usage of adsorption and membrane separation among other processes. The color and the odor may be removed completely after activated carbon treatment. The pretreated water can be passed through a cross flow reverse osmosis membrane system and the permeate water can then be reused.

The typical method to treat Dairy Processing wastewater is as follows:

Stage 1 Emulsion Cracking/pH Adjustment/Precipitation and Coagulation: pH is raised (or lowered) to ~8.5 with the pH controller using caustic (or acid). A coagulant de-emulsifier is added to break any emulsion and cause precipitation of the solids. A “pin floc” is developed indicating the emulsion and the suspended solids are precipitated.

Stage 2 - Flash Mix: The wastewater with it’s precipitated pin floc is introduced to the flash mix zone where a polymer flocculent is added. This stage maximizes flocculent dispersion throughout the coagulated wastewater.

Stage 3 - Flocculation: The wastewater is now introduced to the slow mix zone to agglomerate the floc into larger particles suitable to be enmeshed with the air bubbles.

Clarifier, Dissolved Air Flotation (DAF): The flocculated wastewater is introduced into the DAF inlet where the floc particles are comingled with a pressurized dissolved fine bubble recycle stream. The floc particles attach to the bubbles and float to the surface where they are mechanically skimmed into the float scum sludge chamber. The clarified treated water then exits the end of the DAF and flows downstream to sewer or further treatment if necessary. The DAF system bubbles come from a Recycle Air Dissolving system that takes a portion of treated effluent, pressurizes it and introduces air to be dissolved. The dissolved air comes out of solution and forms a fine bubble stream when the pressure is released at the DAF entrance in the presence of floc wastewater.

DAF Sludge Handling: The resulting DAF waste scum/sludge is removed from the DAF automatically as the scum accumulates and is pumped to the sludge holding tank where it further thickens and accumulates a batch for disposal or processing in a filter press. The sludge is mixed and conditioned with a filter aid such as DE to improve porosity and filterability which will improve cake dryness and prevent premature blinding of the filter cloths.

Sludge Dewatering: The thickened DAF scum/sludge is allowed to accumulate sufficiently to provide a full batch for the Filter Press. The filter press is pumped with the sludge until it is full. The filter press is then emptied of the “cake” which is a semi solid of approximately 20-35 % solids. Sludge cake is high in solids and should be disposed of according to environmental regulations.